The ability to remain mobile is a fundamental contributor to quality of life and is essential for the preservation of independence in old age. Millions of Americans currently report mobility related impairments and these numbers will rise significantly with the aging of our populace. Self-selected walking speed highly correlates with quality of life, functional ability, balance capabilities and is predictive of future health status decline in functional capacity, hospitalization and mortality. As such, therapeutic exercise interventions for older adults with mobility limitations have focused on improving walking as a means to reduce or delay physical disability but with limited success. Herein we propose to explore the efficacy of an innovative advance in physical rehabilitation technology, dual belt treadmill, which is capable of imposing unique propulsive and stability demands independently on each leg during walking. Repetitive locomotor perturbations using the dual belt treadmill forces the central nervous system to solve/adapt (locomotor adaptation) to the challenge using both frontally-mediated locomotor and cognitive resources. Based on exciting preliminary data from our labs, we hypothesize that an intervention that can challenge the locomotor processes required for safe, efficient gait while concurrently providing an aerobic stimulus will produce favorable changes in both gait performance and functional capacity in older adults at risk for mobility disability. To investigate the effects of dual belt training on gait and functional capaciy in those at risk for mobility disability, a two year, single-center, rater-blind exploratory study s proposed. For this pilot feasibility study we will enroll 48 sedentary older adults at risk for disability (usual gait speed = 1.0 m/s and a summary score on the Short Physical Performance Battery (SPPB) 7 - 10) will be randomly assigned to either traditional treadmill exercise (N=16) or dual belt treadmill exercise (N=16) with matched cardiovascular intensities or a control group (N=16). Aim 1 will test the hypothesis that compared with a traditional treadmill intervention dual belt treadmill training will result in greater improvements in gait performance, as reflected by improvements in walking speed and gait variability. Aim 2, an exploratory aim, will test the hypothesis that compared with a traditional treadmill intervention a dual belt treadmill intervention will results in greater improvements in functional capacity (i.e. mobility disability, balance function, functional performance, walking efficiency, and aerobic capacity). To date, no experimental study has evaluated these propositions in a controlled trial. Therefore, results from the proposed pilot study have the potential to be both highly innovative and clinically significant while providing preliminary data for a larger randomized clinical trial.